19 On the evening of that first day of the week, when the doors were locked, where the disciples were, for fear of the Jews, Jesus came and stood in their midst and said to them, “Peace be with you.” 20 When he had said this, he showed them his hands and his side. The disciples rejoiced when they saw the Lord. 21 (Jesus) said to them again, “Peace be with you. As the Father has sent me, so I send you.” 22 And when he had said this, he breathed on them and said to them, “Receive the holy Spirit. 23 Whose sins you forgive are forgiven them, and whose sins you retain are retained.”
24 Thomas, called Didymus, one of the Twelve, was not with them when Jesus came. 25 So the other disciples said to him, “We have seen the Lord.” But he said to them, “Unless I see the mark of the nails in his hands and put my finger into the nailmarks and put my hand into his side, I will not believe.” 26 Now a week later his disciples were again inside and Thomas was with them. Jesus came, although the doors were locked, and stood in their midst and said, “Peace be with you.” 27 Then he said to Thomas, “Put your finger here and see my hands, and bring your hand and put it into my side, and do not be unbelieving, but believe.” 28 Thomas answered and said to him, “My Lord and my God!” 29 Jesus said to him, “Have you come to believe because you have seen me? Blessed are those who have not seen and have believed.” 30 Now Jesus did many other signs in the presence of (his) disciples that are not written in this book. 31 But these are written that you may (come to) believe that Jesus is the Messiah, the Son of God, and that through this belief you may have life in his name. (John 20:19-31)
In the Johannine narrative our gospel occurs on what has been a full day: “On the evening of that first day of the week.” It was only that morning that Mary Magdalene had visited the tomb and confessed, “They have taken the Lord from the tomb, and we don’t know where they put him” (20:2) – ironically echoing one the decisive misunderstanding of Jesus’ ministry: from where did Jesus come and where is he going (e.g. 7:33-36, 8:21-23). Mary became the first disciple of the good news of the empty tomb conveying the word to Peter and “the one whom Jesus loved.” Slowly the implications of the empty tomb and the burial linens come to the disciples and they begin to understand – each in differing ways and to varying degrees. The disciple whom Jesus loved “saw and believed” (20:8), however “they did not yet understand the scripture that he had to rise from the dead” (v.9).
At this point, it is perhaps that their faith is as complete as faith in the empty tomb can be, but as many commentators have noted, to assign to the disciples a full belief in the Resurrection is to rush the story. Resurrection faith begins when Mary encounters Jesus in the garden and he is revealed as the Risen Christ and Good shepherd – he knows his sheep by name and they respond to his voice (10:3-4, 12,16, 24; cf Is 43:1). In telling Mary “stop holding onto me” (v.17) Jesus lets Mary (and the reader) know that the unfolding of the events of the hour are continuing.
You can read a complete commentary on the Gospel here.